Viral Math Problem Asks: When Is Cheryl’s Birthday?
A logic problem from a standardized math test given to students in Singapore has gone viral, with people all over the world struggling to determine the date of Cheryl’s birthday.
Singapore Math Problem Goes Viral
The problem, given to high school students participating in the Singapore and Asian Schools Math Olympiad (SASMO), presents test-takers with a seemingly impossible problem:
“Albert and Bernard just became friends with Cheryl, and they want to know when her birthday is. Cheryl gives them a list of 10 possible dates.
May 15, May 16, May 19
June 17, June 18
July 14, July 16
August 14, August 15, August 17
Cheryl then tells Albert and Bernard separately the month and the day of her birthday respectively.
Albert: I don’t know when Cheryl’s birthday is, but I know that Bernard does not know too.
Bernard: At first I don’t know when Cheryl’s birthday is, but I know now.
Albert: Then I also know when Cheryl’s birthday is.
So when is Cheryl’s birthday?”
The complicated math problem was shared to Twitter, where it went viral and spread confusion across Twitter.
— Dai Lama (@WelshDalaiLama) April 13, 2015
“This is not a math problem; it’s a communication problem!” HAHAHA #cherylsbirthday
— Jaslin Tan (@jaslintan) April 14, 2015
— Katie Chrystler (@kchrystler) April 14, 2015
SPOILER: Cheryl’s Birthday Solution
When the problem first circulated, many inaccurately believed that the question was meant for middle school level students. In fact, according to the Singapore and Asian School Math Olympiads, who wrote the question, the question is “meant to sift out the better students” and appears second to last in the test. Furthermore, the SASMO is meant to challenge the “top 40% of the student population.”
In an effort to keep Singapore parents from worrying about the difficulty level of their children’s education, SASMO released the official solution to the problem, revealing that Cheryl’s birthday is, in fact, July 16!